1. Field of the Invention
The invention relates to round-flat twisted-pair cables, and particularly to an offset arrangement among the neighboring twisted-pairs to reduce the crosstalk therebetween.
2. The Related Art
The round-flat twisted-pair cable (FIG. 8), which is essentially a twisted-pair flat cable (FIG. 7) in a roll manner, can provide some advantages of saving the occupied space and leaving more space for heat transfer airflow as well as for the cable layout inside the chassis for termination efforts, in comparison with the traditional twisted-pair flat cable which inevitably and essentially extends in a plane as shown in U.S. Pat. No. 4,381,426. It is noted the so-called twisted-pair cable essentially refers to the differential pair cable in a twisted manner for each pair thereof.
However, the round-flat twisted-pair cable may inevitably generate a high crosstalk amounted accumulated by not only the neighboring twisted-pairs in the same layer but also the neighboring twisted-pairs in the adjacent upper and lower layers. In the past, there were many kinds of arts to arrange the twisted pairs for twist flat cable for reducing the crosstalk thereof. Some were based upon varied pitches which might cause some non-uniform impedance and propagation dealy. Also, achievement of the cancellation of the crosstalk was required with the common-integer turns of the twisted pairs, which might take a long distance/length of the twisted pairs for complete cancellation. Such a pitch variation method for cancellation of the twisted pairs essentially fit for the low frequency transmission only. Additionally, the pitch variation method required trial-and error to figure out the lay variation for maximum reduction of noise, such as current SCSI round flat cables. When frequency transmission gets higher and higher, it is desired to have a scientific and systematic method. The inventor developed some systematic and scientific methods before for reduction the crosstalk of the flat type twisted pair cable as disclosed in U.S. Pat. No. 6,348,651, and the bundle type twisted pair cable as disclosed in U.S. Pat. Nos. 6,794,570 and 6,825,410, while so far, there is no invention addressing the methodology of the twisted pair arrangement to obtain the best crosstalk performance for the round-flat twisted pair cables.